Editorial

Acute respiratory distress syndrome (ARDS) is a life-threatening organ failure with impairment of pulmonary gas exchange due to several pulmonary and extra-pulmonary injuries. Patients with ARDS have refractory hypoxemia, dyspnea and non-cardiogenic pulmonary edema, generally requiring invasive mechanical ventilation, and acute rescue and supportive therapies. Acute respiratory distress syndrome (ARDS) was first described in 1967 [1]. ARDS was described as “Respiratory distress syndrome” in the past, and it was clinically characterized by the acute onset of severe dyspnea, tachypnea, cyanosis refractory to oxygen, loss of compliance, and infiltration on the chest radiographs.

In 1994, The American-European Consensus Conference (AECC) definition of ARDS defined ARDS by the presence of the following four criteria: 1-acute onset; 2- hypoxemia, as indicated by the ratio of partial pressure of arterial oxygen to fraction of inspired oxygen [PaO2/FiO2] ≤ 200 mmHg; 3-bilateral infiltrates on frontal chest radiograph; 4-absence of left atrial hypertension. ARDS was considered the more severe form of Acute Lung Injury (ALI), defined by the same criteria, but with less severe hypoxemia (PaO2/FiO2 ≤300 mmHg) [2].

After that, the Berlin definition of ARDS was declared in 2012. According to the Berlin definition, ARDS is a form of acute diffuse lung injury occurring in patients with a pre-disposing risk factor, meeting the following criteria: 1-onset within 1 week of a known clinical insult or new/worsening respiratory symptoms; 2-presence of bilateral opacities on the chest radiographs, not fully explained by effusions, lobar/lung collapse, or nodules; 3-diagnosis of respiratory failure not fully explained by cardiac failure or fluid overload, with the need for objective assessment (e.g., echocardiography) to exclude hydrostatic edema if no risk factor is present; 4-presence of hypoxemia, defined by PaO2/FiO2 measured with a minimum requirement for PEEP of ≥5 cmH2O (or non-invasive continuous positive airway pressure ≥5 cmH2O for mild ARDS) and identifying three mutually exclusive categories of severity: mild with 200 mmHg < PaO2/FiO2 ≤ 300 mmHg, moderate with 100 mmHg < PaO2/FiO2 ≤ 200 mmHg, severe with PaO2/FiO2 ≤ 100 mmHg [3,4].

Lorenzo Del Sorbo et al. [5] reported that several important issues were addressed in the Berlin definition of ARDS in an editorial. The often misused term ALI was removed. A specific timing of onset was defined. The need for a predisposing risk factor was incorporated. The exclusion criterion based on the presence of hydrostatic edema was redefined. The radiological criteria were reformulated. The requirement of a minimum PEEP to establish the severity of hypoxemia according to PaO2/FiO2 was introduced. Moreover, the three mutually exclusive categories of mild, moderate, and severe ARDS were validated, as they were associated with increasingly severe disease using mortality, ventilator-free days, and the duration of mechanical ventilation as outcomes in survivors.

Biomarkers in the acute respiratory distress syndrome have been investigated in many studies. But, there are no biomarkers of ARDS in use in clinical practice. In the future, considering technologic advances, pulmonary and extra-pulmonary causes of ARDS a specific biomarker related to ARDS may be established. Furthermore an ARDS Severity Score (ASS) may be described by an international ARDS council (Table 1).

Year

Definition

What is New?

1967

First described

Respiratory distress syndrome

1994

AECC

ARDS was considered the more severe form of ALI, ARDS was PaO2/FiO2 ≤ 200 mmHg